The present invention relates to a steerable nozzle for a reaction engine, i.e. a nozzle which is capable of steering the jet from a reaction engine.
When such a nozzle is mounted on an airplane, it enables the pilot to vary the pitch and yaw of the airplane quickly (and indeed the roll for a two-engined aircraft).
French patent application FR-A-2 470 253 discloses a steerable nozzle comprising a fixed portion secured to an engine and a pivoting portion hinged to the fixed portion and controlled by actuators. The pivoting portion is centered and held relative to the fixed portion by assemblies of resilient elements that are regularly distributed around the circumference of the nozzle and that are disposed in each assembly parallel to the longitudinal axis of the fixed portion. Each of the assemblies is constituted by a fixed resilient element whose base is secured to the fixed portion and whose opposite end is secured to an intermediate ferrule, and a moving resilient element whose base is secured to the pivoting portion and whose opposite end is secured to the intermediate ferrule.
When the pivoting portion is in a position other than its neutral position, i.e. when the jet delivered by the engine and leaving the nozzle is deflected relative to the longitudinal axis of the fixed portion, each assembly of resilient elements is subjected to deformation which has the effect either of moving the bases of the resilient elements apart or else of moving them towards one another. In an extreme position, the base of the moving resilient element comes into abutment against the base of the fixed resilient element, thereby putting a limit on deflection of the moving portion.
The present invention seeks to provide a steerable nozzle in which greater deflection of the pivoting portion can be obtained for given size of the resilient means for centering and holding the pivoting portion.
To this end, the invention provides a steerable nozzle for a reaction engine, the nozzle comprising a fixed portion for fixing to the engine, a moving portion hinged to the fixed portion, control means for controlling the moving portion, and one or more resilient assemblies disposed between the fixed portion and the moving portion, the nozzle being characterized in that each resilient assembly comprises:
at least one fixed resilient stud having a first end secured to the fixed portion and a second end, opposite from the first end, secured to a rigid piece; and
at least one moving resilient stud having a first end secured to the moving portion and a second end, opposite from the first end, secured to said rigid piece;
said at least one fixed resilient stud and said at least one moving resilient stud being offset relative to each other in a circumferential direction of the nozzle.
Thus, in the invention, the moving resilient stud(s) is/are offset relative to the fixed resilient stud(s) in a circumferential direction, i.e. no moving resilient stud is in register with a fixed resilient stud in an axial direction of the nozzle. In the neutral or rest position of the moving portion, the moving resilient stud(s) is/are located downstream from the fixed resilient studs in the axial direction. In an extreme position, the first end of each moving resilient stud comes at least level with the first end of the fixed resilient stud(s) in the axial direction, and when a plurality of fixed resilient studs and a plurality of moving resilient studs are provided, the respective first ends of the moving resilient studs are interposed between the respective first ends of the fixed resilient studs. In this way, for given size of the resilient assembly, the stroke of the moving resilient stud(s) is increased so the deflection of the moving portion of the nozzle is likewise increased.
In a particular embodiment of the invention, each resilient assembly comprises two fixed resilient studs and one moving resilient stud positioned circumferentially (about the nozzle) between the two fixed resilient studs. The rigid piece is V-shaped, with the tip of the V-shape being fixed to the moving resilient stud and the other two ends of the V-shape being respectively fixed to the fixed resilient studs.
In another embodiment of the invention, each resilient assembly comprises two moving resilient studs and one fixed resilient stud positioned circumferentially (about the nozzle) between the two moving resilient studs. The rigid piece is V-shaped, with the tip of the V-shape being fixed to the fixed resilient stud and the other two ends of the V-shape being respectively fixed to the moving resilient studs.
Typically, the moving portion is hinged to the fixed portion by ball-and-socket forming means which comprise a fixed spherical bearing surface and a moving spherical bearing surface that is slidable over the fixed spherical bearing surface. The moving spherical bearing surface is connected to the control means. In addition, the first end of the or each fixed resilient stud is fixed to the fixed spherical bearing surface and the first end of the or each moving resilient stud is fixed to the moving spherical bearing surface. More particularly, the or each moving resilient stud is fixed to a projection from the moving spherical bearing surface, said projection being of a shape and a size that enables it to be interposed between two fixed resilient studs.
The control means used for controlling the displacements of the moving portion relative to the fixed portion preferably comprise actuators regularly distributed around the circumference of the nozzle.
The fixed and moving resilient studs are preferably made of a laminated material capable of withstanding the temperature that exists in the nozzle. The laminated material is constituted by a stack of alternating layers of elastomer and metal, a stack of alternating layers of elastomer and an organic composite material, or a stack of alternating layers of elastomer and a thermostructural material. The elastomer is selected from elastomers capable of withstanding temperatures greater than 150xc2x0 C. By way of example, an elastomer is used that is selected from fluorocarbon and fluorosilicone materials, and from hydrogenated elastomers such as hydrogenated nitril butadiene rubber (HNBR).
The nozzle of the invention can also have steerable flaps secured to the moving portion. By way of example, the steerable flaps can constitute a converging-diverging assembly. Under such circumstances, the flaps are steered in particular to modify the diameter of the nozzle throat, i.e. the diameter of the cross-section defined between the converging flaps and the diverging flaps of the converging-diverging assembly.